Physcia caesia #

Taxon #

Physcia caesia

Organization #

Physciaceae

Identification #

Physcia caesia is a very common species of rock dwelling lichen which can be quickly recognized, although there are a few lookalikes. P. caesia forms attractive, light to dark gray thalli which can turn a light bluish or greenish when well-hydrated. Mature specimens will have convex to spherical, gray soralia which are better developed closer to the center of the thalli. It will rarely produce apothecia with black discs and rims which are concolorous with the thalli. Physcia dubia is perhaps the most similar but has labriform soralia rather than the convex, capitate soralia found in P. caesia. P. biziana is another grayish saxicolous Physcia but it lacks soredia. P. stellaris is a corticolous species and is usually abundantly apotheciate (CLH).

Substrate #

usually saxicolous, also on bone (Spribille et al. 2023), and rarely lignicolous or corticolous (CLH, Brodo et al. 2001).

Chemical Tests #

upper cortex and medulla: K+ yellow, C-, KC-, Pd+ yellow (CLH)

Notes #

Ubiquitous throughout Alaska.

Photos #